by volume occurred at to 70 m. and 38 per- 

 cent at 70 to 140 m. (Holmes, MS., see foot- 

 note 1). Blackburn (1966) used data from 

 Klawe (1961) to show the regression of the 

 standing crop of zooplankton at to 300 m. 

 on that at to 140 m., and vice versa, for 

 pairs of hauls made one after the other at each 

 of 24 stations. About 80 percent of the crop at 

 to 300 m. was located at to 140 m., on 

 average, by day or night. These data, together 

 with those of Holmes, suggest a general dis- 

 tribution of zooplankton for the to 300 m. 

 water column in the eastern tropical Pacific 

 as follows: to70m.,50percent;70 to 140 m., 

 30 percent; and 140 to 300 m., 20 percent. 



Practically no useful information has been 

 published on the vertical distribution of the 

 standing crop of micronekton m the eastern 

 tropical Pacific since only the to 90 m. 

 depth range has been covered in routine 

 hauls. 



observations (which were considered to in- 

 dicate conditions in the same surface water 

 body or water type) close to the drogue. 

 For small zooplankton without salps, night 

 catches (milliliters per 1,000 m.^) averaged 

 about twice as high as day catches. For all 

 zooplankton including salps, night catches 

 were up to 10 times, and on average 3 or 

 4 times, as high as day catches. These 

 hauls were all oblique to a depth of about 

 300 m. 



Blackburn (MS., see footnote 2) tabulated 

 measurements of standing c rop of mic ronekton 

 (milliliters per 1,000 m.3) at about noon and 

 midnight on the successive days of operation 

 27; midnight catches were consistently 5 to 10 

 times higher than noon catches; noon catches 

 consisted almost entirely of crustaceans, 

 whereas midnight catches included typical 

 night-rising mesopelagic fishes and cepha- 

 lopoda as well. 



VARIATION IN BIOLOGICAL PROPERTIES 

 B^ TIMES OF DAY 



The emphasis m most oceanographic cruises 

 in the eastern tropical Pacific has been so 

 strongly on areal coverage, that little time 

 was available for repeated observations at 

 different times of day at particular stations. 

 A few observations of this kind have been made, 

 however. Holmes and Haxo (1958) made two 

 series of observations on surface primary 

 productivity (C'"* method incubated under con- 

 stant artificial illumination) of samples taken 

 every 2 or 3 hours at the same station over a 

 24-hour period. It was clear from both experi- 

 ments that photos>"nthesis was less between 

 1800 and 0200 hours than at other times of 

 day. The daily maximum was at 0800 to 1000 

 in one experiment; in the other experiment, 

 which was imperfect, the maximum could have 

 occurred at about the same time. The vari- 

 ability of surface chlorophyll a_ with time of 

 day, investigated when the second productivity 

 experiment was being made, showed the con- 

 centration to be "fairly constant." Shimada 

 (1958), who nneasured surface productivity and 

 surface chlorophyll a at a station over a 46- 

 hour period, found that both were maximal in the 

 early morning (about 0600 to 0900 hours) and 

 minimal at about 1800. Maxima and minima dif- 

 fered for productivity by a factor of about five, 

 and for chlorophyll^ by a factor of about two. 



The largest set of observations on diurnal 

 change in standing crop of zooplankton is from 

 operation 27 (Griffiths, MS.^ ), on which the 

 ship followed a drifting surface parachute 

 drogue about 20 days and made repetitive 



'Griffiths, Raymond C. The variability of the volumes 

 of zooplankton taken in oblique, paired, one-meter net 

 hauls. (Scripps Institution of Oceanography, University of 

 California, 1963). 



VARIATION IN BIOLOGICAL PROPERTIES 

 ON SUCCESSIVE DAYS 



On operation 27 several biological properties 

 were measured at the same time or times of 

 day on about 20 successive days, as de- 

 scribed in the preceding section. Holmes (MS., 

 see footnote 1) made rank-difference correla- 

 tion tests for time -correlated trends of stand- 

 ing crop of chlorophyll a measured at about 

 noon each day for 2 m. below the surface, the 

 isothermal layer (total), and to 7 1 m. (total). 

 Only the isothermal layer showed significant 

 time-correlation (positive); this correlation 

 was attributed to the deepening of the iso- 

 thermal layer during the experiment. Griffiths 

 (MS. b, see footnote 3), who made an analysis 

 of variance of logarithms of standardized 

 zooplankton volumes for different effects, in- 

 cluding day and time of day, found a significant 

 interaction between day and time of day; for a 

 shorter period of days, in which the inter- 

 action between day and time of day was not 

 significant, both day and time-of-day effects 

 were significant. Blackburn (MS., see foot- 

 note 2) tabulated standardized micronekton 

 volumes for the successive days of the same 

 experiment, separately for noon and midnight; 

 volumes on some days differed from those on 

 other days by factors up to three. It should be 

 made clear that operation 27 was deliberately 

 carried out in a time-space situation in which 

 it was thought that temporal changes in proper- 

 ties would be small. 



Over the period of the same experiment, 

 highly significant positive correlation coeffi- 

 cients (>0.8) were obtained between the three 

 noon measurements of chlorophyll a_mentioned 

 above, both with and without transformation of 

 the data into logarithms (Holmes, MS., see 

 footnote 1). 



